Wireless communication systems may include a multi-RAT UE having capability to access two or more radio access technologies (RATs) or communication systems. To access a specific RAT, connection to the specific RAT is established on the basis of a UE request and transmission/reception of data is performed. However, a multi-RAT UE cannot simultaneously access multiple RATs even if the multi-RAT UE has capability to access two or more RATs. That is, the multi-RAT UE cannot simultaneously transmit and receive data through different RATs even if the UE has multi-RAT capability.
Since the conventional multi-RAT scheme does not require interworking between a wireless LAN and a cellular network, system efficiency thereof is low. In addition, the conventional multi-RAT scheme supports only flow mobility/IP-flow mapping at a network level without control at a radio level even if a UE can simultaneously access multiple RATs, thereby enabling simultaneous access to multiple RATs. For this reason, the conventional scheme has been performed on the basis of a request of the UE without requiring control connection between an AP and a cellular network.
However, such conventional scheme selects RATs for a UE without recognizing an accurate network state, and thus there is a limitation in enhancement of network efficiency. Particularly, as UEs can access multiple communication systems, UEs requires methods to perform efficient data switching from a specific communication system to another communication system. However, research thereon has not been performed.